Point-contact diode with au-pt point



Nov. 28, 1967 A. GAUDLITZ Filed Aug. 24, 1964 DOPED REGION --'2 l.-SPRING WIRE (M0 or W) 5PO|NTED END (Au-P1 ALLOY) 3P-N JUNCTION' P'MONOCRYTALLINE SEMICONDUCTOR 4 Claims. (ci. 317--236) My invention relates to point-contact diodes having a monocrystalline semiconductor body, preferably of germanium, contacted by the pointed end of a spring wire consisting of molybdenum or tungsten, the point being joined or fused to the semiconductor body.

Wires or whiskers of molybdenum or tungsten possess a particularly favorable spring action in point-contact diodes. However, it is often desirable, particularly for ultra-high-frequency diodes, to employ a whisker material, such as platinum, which forms recombination centers in the semiconductor body when diffusing into the crystal during the formation process employed for joining the contact point to the body. n the other hand, using a spring of platinum entails the disadvantage that, due to the softness of this material, the point becomes bent or otherwise deformed when being pressed against the semiconductor surface and particularly when subsequently subjected to the formation treatment, thus resulting in too large a. contacting area. Such enlargement of the point area impairs the properties of the diode, particularly those required for UHF applications, because it increases the diode capacitance and thus reduces the upper frequency limit of the device, aside from the fact that the mechanical stability of the contacting bond obtained when attaching a platinum wire leaves much to be desired.

It is an object of my invention to eliminate these shortcomings and to provide a point-contact diode Which affords using recombination-center metal for the spring wire while preventing an increase in contacting area and hence in capacitance, thus improving the UHF-properties of the diode; and it is also an object of the invention to secure a satisfactory mechanical stability of the contact junction.

According to the invention, the spring or whisker of the point-contact diode consists of a molybdenum or tungsten wire which is coated, at least at the pointed end, with a gold alloy which contains mainly platinum as its further constituent.

Such a point-contact diode according to the invention exhibits a good elasticity and can readily be given a point of the desired small radius. The hard point is not appreciably deformed during the forming treatment by means of which the point is fused or welded to the semiconductor body.

Preferably the gold-platinum alloy of the coating contains about 3 to by weight of platinum, the remainder being substantially all gold, with the exception of any desired doping additions which, if present, constitute only slight small quantities such as in the order of 1 to 2% or fractions thereof.

The drawing shows by way of example and in cross section a point-contact diode according to the invention on enlarged scale.

The semiconductor 1 or the illustrated diode consists, for example of n-type germanium. An elastic spring wire 4 has its pointed end 5 placed upon the top surface of the fiat and circular semiconductor disc. The wire 4 consists of molybdenum or tungsten and is coated entirely or at least at the pointed end, with the abovementioned goldplatinum alloy. As will be more fully described below, the wire 4 is jointed at the pointed end 5 with the semi conductor body 1 by a forming treatment which involves United States Patent 0 3,355,638 Patented Nov. 28, 1967 the application of heat to cause fusing of the gold.- platinum coating to the semiconductor material. During this treatment, a p-type region 2 is formed in the semiconductor body 1 and results in the formation of a pm junction 3 within the body 1. Simultaneously, the alloying constituents ditfuse into the contacted region of the semiconductor body. To secure proper p-type doping of the region 2, an acceptor such as indium or gallium may be added to the gold-platinum alloy in accordance with conventional doping technique.

When the semiconductor body is of p-type conductance, a donor substance, such as antimony, is added to the goldplatinum alloy to produce in the semiconductor body an n-type region adjacent to the contact point.

The semiconductor body 1 is preferably joined at its bottom surface with a plate or housing portion (not illustrated) of good heat conducting metal, for example copper.

Aside from the above-mentioned advantages, a diode according to the invention, as exemplified by the illustrated embodiment, involves further improvements on account of the gold content of the alloy. At the temperatures employed for the formation treatment, the gold readily converts to liquid constitution, it alloys very well with the material of the semiconductor body, and very rapidly diffuses into the body. Particularly when the semiconductor body consists of germanium, gold forms with the semiconductor material a eutectic composition, at relatively low temperatures.

As mentioned, the gold-platinum alloy may also contain doping substances, for example acceptors such as In, Ga or donors such as Sb. Additionally, substances which form recombination centers may also be admixed to the alloy, for example Ni or Cu. The latter substances may also be added to the alloy in lieu of doping substances, particularly if the recombination-center forming metals themselves have a doping action upon the semiconductor material.

In cases where the gold-platinum alloy contains further constituents as mentioned above, the gold acts essentially as a carrier for these additional substances. That is, due to its good alloy ability with the semiconductor material, the gold content of the alloy promotes the penetration of the other alloying constituents into the semiconductor body.

The spring wires for diodes according to the invention are preferably made simply by immersing a thin wire of molybdenum or tungsten into the liquid gold-platinum alloy, either entirely or only at the pointed end, and thereafter withdrawing the wire; this suffices to coat the wire with the solidifying alloy.

Thereafter the point-contact diode according to the invention is produced by placing the point end of the alloycoated spring upon the top surface of the semiconductor body and holding it in contact therewith. A current surge is then passed through the spring and the semiconductor body so that the gold-platinum alloy is liquefied, particularly only at the pointed end of the spring, and becomes alloyed with the material of the semiconductor body and also diffuses into the body. For example, the wire may have 0.1 mm. diameter and presses its point against the silicon body under a spring force of about 0.5 gram. By applying a current of 500 ma. for 20 in. sec., the desired formation is reliably obtained. The high temperatures electrically produced during the forming treatment particularly cause the gold to readily alloy with the semiconductor material, and a sufficient amount of gold diffuses into the crystal to produce a contact of high mechanical strength. In comparison with the alloying of a wire consisting of gold only, the method of the invention affords the advantage that the cross section of the contact and consequently the capacitance of the device are not detrimentally increased. Since platinum simultaneously diffuses into the crystal, it furnishes the desired recombination centers Which shorten the relaxation time of the diode.

The invention is applicable in the same manner to other semiconductor materials, for example silicon.

I claim:

1. A point-contact diode comprising a monocrystalline body of semiconductor material, a spring wire having a pointed end contacting said body and joined therewith, said wire being of metal from the group consisting of molybdenum and tungsten and having at least on said pointed end a coating formed of a gold-platinum alloy containing 3 to 10% by weight of platinum, the remainder being substantially all of gold.

2. In a point-contact diode according to claim 1, said alloy coating containing an addition of doping substance.

3. In a point-contact diode according to claim 1, said alloy coating containing an addition of recombinationcenter forming substance.

4. A point-contact diode comprising a monocrystalline body of germanium, a spring wire having a pointed end contacting said body and joined therewith, said wire hav- 4 ing on said pointed end a coating of an alloy formed of about 90 to 97% by weight of gold and about 3 to 10% of platinum, said alloy containing an addition of dopant, said pointed end being merged with said germanium body, and said body having adjacent to said pointed end a region doped by said dopant and forming a p-n junction in said body.

References Cited UNITED STATES PATENTS 1,104,073 7/1914 Pickard 317-236 2,402,839 6/1946 Ohl 317-236 2,429,222 10/ 1947 Ehrhardt et a1. 317236 X 2,818,536 12/1957 Carman et al. 317236 2,820,135 1/1958 Yakmakawa 317-236 X 2,876,400 3/1959 Gunther 317236 X 2,984,890 5/1961 Hambor et al. 317236 X 3,254,279 5/1966 Cohn et al. 317236 JOHN W. HUCKERT, Primary Examiner.

A. M. LESNIAK, Assistant Examiner. 

1. A POINT-CONTACT DIODE COMPRISING AMONOCRYSTALLINE BODY OF SEMICONDUCTOR MATERIAL, A SPRING WIRE HAVING A POINTED END CONTACTING SAID BOYD AND JOINED THEREWITH, SAID WIRE BEING OF METAL FROM THE GROUP CONSISTING OF MOLYBDENUM AND TUNGSTEN AND HAVING AT LEAST ON SAID POINTED END A COATING FORMED OF A GOLD-PLATINUM ALLOY CONTAINING 3 TO 10% BY WEIGHT OF PLATINUM, THE REMAINDER BEING SUBSTANTIALLY ALL OF GOLD. 